Allochromatic gems are gems which can be coloured by impurities. Whenever they ended up wholly pure, they might be colorless. The color of all allochromatic gems is made by defects. Hence, all coloration in corundum is caused by defects. Certification: The presence of a reputable gemological certification from a dependable https://www.tumblr.com/thegemjournal/759696203354128384/understanding-the-unique-characteristics-of-yellow?source=share